THIS INVENTION relates in particular but is not limited to a security fence.
Security fences are commonly known barriers to restrict or prevent the access or egress of unauthorised persons to or from a fenced area such as for the protection of property and belongings. Security fences are also used to confine persons such as inmates of a prison or detainees of a detention centre to a confined area. The effectiveness of prior art security fences is often limited to the height of the fence and whether the fence includes other barriers or obstacles such as barbed wire or razor wire to deter climbing over them. In many cases security fences with such barriers can often be overcome by simply placing a heavy mat or similar material over the barbed wire or razor wire. In order to overcome this problem, prior art security fences often have a barrier of barbed wire at the top of the fence which is also angled away from the fence. Commonly, the fence may in fact have two barriers of barbed wire in a Y shaped configuration to make the fence more difficult to climb across. Even where the Y shaped barrier is used, determined climbers can still cross these barriers by placing heavy mats over them.
Australian Patent No. 237170 describes a flexible guide post employing a coil spring fitted into a concrete footing. U.S. Pat. No. 4,605,204 describes a collapsible recreational fence employing a resilient plastics mesh with plastic posts. German Patent No. DE 3834817 describes a security fence with small springs allowing limited deflection of an upper part of the fence to activate a microswitch to detect intruders. UK Patent No. 1354057 describes a security fence where strain gauges detect interference with the fence. U.S. Pat. No. 1,336,680 describes a fence post used to allow passage of driftwood to prevent the fence being damaged during floods. U.S. Pat. No. 5,597,262 describes a resiliently deflectable traffic bollard with rotatable collar.
While the above referenced patents describe various forms of post and fence deflections they are either expensive to manufacture or are unsuitable as part of a security fence of the chain wire type. The present invention provides a security fence that is economical to construct as an alternative to existing security fences and provides a resiliently deflectable upper portion positioned above head height secured to a rigid lower portion to inhibit unauthorised persons from climbing over the fence.
It is therefore an object of the invention to overcome to some degree the problems associated with prior art security fences.
In a preferred aspect the invention resides in a security fence having the improvement of fence posts comprising upper and lower portions; the portions connected by a flexible member biased to keep the upper portion in one position relative to the lower portion, wherein in operation, force or weight applied to the upper portion causes the upper portion to collapse in the direction of the force or weight; the upper portion returning to its original position on removal of the force or weight.
Preferably there is provided a security fence comprising spaced posts extending above adult head height, each post having an upright rigid lower portion and a resiliently deflectable upper portion, a major portion of the length of said posts comprising the lower portion and the upper portion having a lower marginal section thereof above head height, barrier material interconnecting the lower portions of adjacent posts to prevent unauthorised access other than by passing over the security fence, barrier means interconnecting the upper portions of adjacent posts, the upper portions resiliently deflecting under load to inhibit unauthorised passage over the security fence. Preferably the upper portion is joined to the lower portion by a resilient connector. Preferably the resilient connector comprises a coil spring and coupling collars extending over marginal end portions of the coil spring and coupling opposite ends of the coil spring to the upper and lower post portions respectively.
Preferably the upper portions comprise Y-shaped terminal sections with barrier means extending between respective arms of said Y-shaped terminal portions of adjacent posts.
Preferably the upper portions are adapted to deflect through an angle of greater than 45xc2x0.
In another preferred aspect the invention resides in a security fence comprising:
at least two spaced upright posts;
the posts having an upper portion and a lower portion;
the upper and lower portions connected by a flexible member biased to keep the upper portion in one position relative to the lower portion;
a panel member spanning between the lower portions of the posts;
a barrier member spanning between the upper portions of the posts, wherein in operation, force applied to the barrier member or the upper portion of the posts causes the barrier member and the upper portion to collapse in the direction of the force;
the barrier member and the upper portions returning to their original position on removal of the force or weight.
Preferably the posts are galvanised iron of circular or square cross sectional profile.
The upper portion is preferably shorter in length than the lower portion of the posts. The upper portion may be in vertical alignment with the lower portion or may be angled away from the lower portion. In the alternative, the upper portion may comprise of two or more sections of post, the sections splayed relative to each other in a V or Y shaped configuration.
In preference the flexible member which biases the upper portion to remain in one position relative to the lower portion of the posts is a coiled spring however other types of flexible members may be used.
Preferably the flexible member is connected to the upper and lower portions by one-way security fasteners which require a special tool for their installation and removal. Other methods of connection such as welding the flexible member directly to the upper and lower portions may also be used. Alternatively, if ordinary fasteners such as hexagonal nuts and bolts are used, the nuts maybe deformed or burred over to discourage removal.
Suitably the barrier member comprises one or more rows of barbed wire or razor wire.
Preferably the panel member is wire mesh however timber or other panel material may be used.